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Use of Virtual Monochromatic Images in a Radiotherapy Clinic

A Romano1*, R Tolakanahalli2 , (2) Walker Family Cancer Centre, St. Catharines, ON


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: DECT synthesized low-energy scans would improve contrast without sacrificing signal-to-noise ratio (SNR). While the lower monochromatic images could be used for accurate tumour delineation, non-contrast basis material image or high energy monochromatic image could be used for dosecalculation. The objective of this study was to study the difference of Hounsfield Units (HU) to electrondensity calibration for synthesized virtual monochromatic images (VMI) ranging from 40 keV to 190 keVand to assess the feasibility of using the VMIs for dose calculation.

Methods: A Gammex-RMI tissue characterization phantom was scanned using a Siemens AS-40Somatom MDCT. The phantom has interchangeable inserts made of epoxy-based tissue substitutes.Scans of the phantom were performed using DECT scanning protocols using 80 kvP and 140 kvPpolyenergetic spectra. VMIs were generated using basis material decomposition in the image domainwith water and iodine as the basis materials. The dosimetric impact of variation in the image value todensity table (IVDT) was studied on different radiation treatment plans for an anthropormorphicphantom.

Results: A VMI synthesized at 50 keV was shown to have enhanced contrast with comparable noisecharacteristics when compared to a clinical 120 kvP image. The VMIs and the clinical scans were foundto have different IVDTs with the greatest difference occurring for denser materials such as cortical bone.The dosimetric impact of the difference in IVDT was found to be no more than 1% at D95 of the PTV,with the greatest difference being observed near bone.

Conclusion: VMIs created using DECT scanning protocols are dosimetrically viable to use for radiationtreatment planning.The VMIs can have improved visual characteristics with comparable noise to a clinical scan and are within 1% of the dose when compared to a plan created using a single polyenergetic CT scan.


Dose Volume Histograms, Dual-energy Imaging, Image Processing


IM- CT: Dual Energy and Spectral

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